The present invention relates to a novel polymer, particularly a novel electroconductive polymer and a precursor thereof.
As polymers used for forming electroconductive polymers there are known polyacetylenes, polyparaphenylenes, polythiophenes and polypyrroles. These polymers become employable as electroconductive polymers by being doped using certain kinds of compounds. However, the electroconductive polymers thus obtained are apt to change in quality, especially electrical characteristics, in the air. Further, those polymers are poor in meltability and solubility so are extremely inferior in processability. These drawbacks cause a large obstacle to their practical use. For example, as an application of such electroconductive polymers there has been proposed an application to electrodes for a secondary battery utilizing their reversible redox characteristic. In most cases, however, they are unstable physically or chemically in the electrolyte of a secondary battery. Therefore, it is impossible to expect a stable cyclability of charge and discharge which is a base performance required for a secondary battery. Besides, electroconductive polymers are insoluble and unmeltable because their skeleton is constituted by a .pi. electron conjugated system, and this point is also a serious obstacle to their practical use. As a solution to these-problems there has been proposed in U.S. Pat. No. 4,505,844 an electroactive polymer obtained by doping a polymer having a 3,10-phenoxazinediyl structure as a repeating unit, using an electron acceptor. However, such a phenoxazine polymer is an oligomer of a low polymerization degree, lacking in mechanical strength and moldability which the polymer should possess as a high polymer. For example, in the case of using this polymer as an electrode material of a secondary battery, a soluble component will dissolve out with repetition of charge and discharge, so it is impossible to expect a stable cyclability.
Moreover, in order to impart mechanical strength and moldability to such phenoxazine polymer in addition to good electrochemical characteristics, it is necessary to obtain a polymer higher in the degree of polymerization (a high polymer). But it is difficult to obtain a high polymer even according to any of processes commonly used for the preparation of polyaromatic compounds or polyheteroaromatic compounds, such as Grignard coupling, oxidative coupling, Friedel-Crafts reaction and electrolytic oxidation polymerization. Even under severer reaction conditions, not only it is impossible to expect the realization of a higher molecular weight due to an induced hetero-linkage or crosslinking reaction, but also the polymer becomes incapable of dissolving and melting with loss in processability which is one of the advantages of high polymers. Further, the polymer becomes inactive electrically.
Also, it has been reported that a polymer having a 3,6-N-methylcarbazolyl methylene structure as a repeating unit is soluble in an organic solvent and it exhibits a direct current electroconductivity of about 10.sup.-3 S/cm when doped with an electron acceptor [Synthetic Metals, 10, pp.281-292 (1985)].
However, the above carbazolyl methylene polymer has the drawback that it does not have a reversible doping characteristic or a reversible redox characteristic because the doping causes elimination of hydrogen of methylene in the main polymer chain. Therefore, improvement on this point has been desired.